The long-range objective of this research program is to determine the nature and mechanisms by which the central nervous system controls the volume and composition of the extracellular fluid. Experimental approaches include acute and chronic lesion studies of putative central receptor mechanisms, their effect upon normal fluid and electrolyte balance as well as the response to various osmotic and saline stresses, with the composition of body fluids and renal excretory patterns the principal monitores variables. They will also include stimulation experiments to mimic the effect of peripheral afferent pathways, and as a way of mapping out central pathways and locating integrative regions. In addition to electrical stimuli, specific saline and osmotic stimuli will be used in the general and regional circulations, and directly into the brain and ventricular system.